linux-kernel - Re: [PATCH 1/3] hwmon: (dell-smm) Avoid unnecessary SMM calls during init

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Date:   Tue, 26 Apr 2022 13:33:25 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Armin Wolf <W_Armin@....de>
Cc:     pali@...nel.org, jdelvare@...e.com, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] hwmon: (dell-smm) Avoid unnecessary SMM calls during
 init

On Tue, Apr 26, 2022 at 01:20:48PM -0700, Guenter Roeck wrote:
> On Tue, Apr 26, 2022 at 10:03:18PM +0200, Armin Wolf wrote:
> > When the driver tries to detect the fan multiplier during
> > module initialisation, it issues one SMM call for each fan.
> > Those SMM calls are however redundant and also try to query
> > fans which may not be present.
> > Fix that by detecting the fan multiplier during hwmon
> > initialisation when no extra SMM calls are needed.
> > Also dont assume the last nominal speed entry to be the
> > biggest and instead check all entries.
> > 
> > Signed-off-by: Armin Wolf <W_Armin@....de>
> > ---
> >  drivers/hwmon/dell-smm-hwmon.c | 37 +++++++++++++---------------------
> >  1 file changed, 14 insertions(+), 23 deletions(-)
> > 
> > diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
> > index 30b6f0c28093..202ee884de9e 100644
> > --- a/drivers/hwmon/dell-smm-hwmon.c
> > +++ b/drivers/hwmon/dell-smm-hwmon.c
> > @@ -50,7 +50,7 @@
> >  #define I8K_SMM_GET_DELL_SIG2	0xffa3
> > 
> >  #define I8K_FAN_MULT		30
> > -#define I8K_FAN_MAX_RPM		30000
> > +#define I8K_FAN_RPM_THRESHOLD	1000
> >  #define I8K_MAX_TEMP		127
> > 
> >  #define I8K_FN_NONE		0x00
> > @@ -326,7 +326,7 @@ static int __init i8k_get_fan_nominal_speed(const struct dell_smm_data *data, u8
> >  	if (data->disallow_fan_support)
> >  		return -EINVAL;
> > 
> > -	return i8k_smm(&regs) ? : (regs.eax & 0xffff) * data->i8k_fan_mult;
> > +	return i8k_smm(&regs) ? : (regs.eax & 0xffff);
> >  }
> > 
> >  /*
> > @@ -776,6 +776,7 @@ static int dell_smm_read(struct device *dev, enum hwmon_sensor_types type, u32 a
> >  			 long *val)
> >  {
> >  	struct dell_smm_data *data = dev_get_drvdata(dev);
> > +	int mult = data->i8k_fan_mult;
> >  	int ret;
> > 
> >  	switch (type) {
> > @@ -804,11 +805,11 @@ static int dell_smm_read(struct device *dev, enum hwmon_sensor_types type, u32 a
> > 
> >  			return 0;
> >  		case hwmon_fan_min:
> > -			*val = data->fan_nominal_speed[channel][0];
> > +			*val = data->fan_nominal_speed[channel][0] * mult;
> > 
> >  			return 0;
> >  		case hwmon_fan_max:
> > -			*val = data->fan_nominal_speed[channel][data->i8k_fan_max];
> > +			*val = data->fan_nominal_speed[channel][data->i8k_fan_max] * mult;
> > 
> >  			return 0;
> >  		case hwmon_fan_target:
> > @@ -819,7 +820,7 @@ static int dell_smm_read(struct device *dev, enum hwmon_sensor_types type, u32 a
> >  			if (ret > data->i8k_fan_max)
> >  				ret = data->i8k_fan_max;
> > 
> > -			*val = data->fan_nominal_speed[channel][ret];
> > +			*val = data->fan_nominal_speed[channel][ret] * mult;
> > 
> >  			return 0;
> >  		default:
> > @@ -1071,6 +1072,13 @@ static int __init dell_smm_init_hwmon(struct device *dev)
> >  				break;
> >  			}
> >  			data->fan_nominal_speed[i][state] = err;
> > +			/*
> > +			 * Autodetect fan multiplier based on nominal rpm if multiplier
> > +			 * was not specified as module param or in DMI. If fan reports
> > +			 * rpm value too high then set multiplier to 1.
> > +			 */
> > +			if (!fan_mult && err > I8K_FAN_RPM_THRESHOLD)
> > +				data->i8k_fan_mult = 1;
> >  		}
> >  	}
> > 
> > @@ -1359,7 +1367,6 @@ static int __init dell_smm_probe(struct platform_device *pdev)
> >  	struct dell_smm_data *data;
> >  	const struct dmi_system_id *id, *fan_control;
> >  	int ret;
> > -	u8 fan;
> > 
> >  	data = devm_kzalloc(&pdev->dev, sizeof(struct dell_smm_data), GFP_KERNEL);
> >  	if (!data)
> > @@ -1414,24 +1421,8 @@ static int __init dell_smm_probe(struct platform_device *pdev)
> >  		dev_info(&pdev->dev, "enabling support for setting automatic/manual fan control\n");
> >  	}
> > 
> > -	if (!fan_mult) {
> > -		/*
> > -		 * Autodetect fan multiplier based on nominal rpm
> > -		 * If fan reports rpm value too high then set multiplier to 1
> > -		 */
> > -		for (fan = 0; fan < DELL_SMM_NO_FANS; ++fan) {
> > -			ret = i8k_get_fan_nominal_speed(data, fan, data->i8k_fan_max);
> > -			if (ret < 0)
> > -				continue;
> > -
> > -			if (ret > I8K_FAN_MAX_RPM)
> > -				data->i8k_fan_mult = 1;
> > -			break;
> > -		}
> > -	} else {
> > -		/* Fan multiplier was specified in module param or in dmi */
> > +	if (fan_mult)
> 
> Might as well drop the if statement here.
> 
Never mind, I see that is removed later anyway.

Guenter

> >  		data->i8k_fan_mult = fan_mult;
> > -	}
> > 
> >  	ret = dell_smm_init_hwmon(&pdev->dev);
> >  	if (ret)
> > --
> > 2.30.2
> >